Conveyors have long been recognized as extremely useful devices for transferring a wide variety of objects from one place to another. As a result, many different types of conveyors have been provided. For example, belt and screw conveyors have been provided for transferring raw materials such as mineral ore, coal or grain. Chain conveyors have been provided for transferring automobile components or other component parts in assembly lines. Pneumatic conveyors have been provided for transferring bulk materials such as granulated or pulverized chemicals.
Each of these and other prior art conveyors conventionally provide a fixed loading station, a fixed transfer section and a fixed discharge station. As a result, the object to be transferred by the conveyor must first be delivered to the loading station where it is placed onto the conveyor. After traversing the length of the transfer portion, the object arrives at the discharge station where it must be removed from the conveyor.
Operation of a conveyor is, preferably, constant. Thus, so long as objects are placed upon the loading station, they will be delivered to the discharge station at a constant rate. In order to insure smooth operation of the entire or that portion of the conveyor, objects must be removed from the discharge station at least as quickly as they are loaded onto the conveyor. Otherwise, the discharge station will overflow, causing the conveyor to jam and possibly causing objects to fall from the discharge station.
In an effort to solve the jamming problem, accumulating conveyors were developed. An accumulating conveyor senses that the discharge station (or an intermediate position) is full and must be cleared. In response to this sensed condition, operation of the conveyor ceases until the discharge station (or the intermediate position) is cleared. These accumulating transfer conveyors were provided with reciprocating drive mechanisms that advanced an object along the length of the conveyor.
One such accumulating conveyor is shown by U.S. Pat. No. 3,322,259, issued to C. J. Milazzo. The Milazzo conveyor provides a reciprocating carriage that moves lengthwise of a frame. The frame is divided into two longitudinal sections, with the carriage reciprocating therebetween. An article sensor is provided at various positions on the carriage for sensing the presence or absence of an article on the frame. In a manner common to that of many other prior art accumulating conveyors, a first embodiment disclosed by Milazzo provides a pusher member that, in response to the detection of an article by the article sensor, engages the backside of an article and pushes it along the frame. A second embodiment disclosed by Milazzo provides a plurality of independent lifting plates that, in response to an electronic sensing mechanism, rise to lift and carry articles along the frame from one position to another.
Yet other conveyors have been provided that are similar in operating concept. For example, U.S. Pat. No. 3,385,418 discloses an accumulating transfer conveyor having a pair of parallel transfer bars mounted for reciprocal movement. A detector plate is provided for sensing an article on the conveyor. In response to the detector plate, a plurality of longitudinally aligned, pivotally mounted pushers are provided to engage the trailing edge of the article and move it along the conveyor. Additionally, a set of control pushers are provided to insure that no additional articles are moved unless a particular station has been cleared. Other conveyors employing a sensing device and pushers or the like are shown by U.S. Pat. Nos. 3,527,338; 3,794,158; and 4,314,630.
These and the many other like conveyors in the art suffer from one or more of a number of disadvantages. A principal disadvantage is that such prior art conveyors primarily sense and transfer an object by its backside or its trailing edge. This arrangement mandates that the objects transferred be limited to a certain size. For example, if an article being transferred on a conveyor according to the first embodiment of Milazzo extends beyond the position of a pusher, that pusher is rendered useless to move the article along the frame. If an article being transferred on a conveyor according to the second embodiment of Milazzo is so small as to fit within the spaces between lifting plates, the article may never be moved.
Yet another disadvantage of such conveyors is that they depend on a fixed or stationary frame to support the load. As a result, the loading station and the discharge station are also fixed, necessitating that the objects or articles to be transferred be first delivered to the loading station and then removed and taken from the discharge station. In many circumstances, this problem is so acute as to require two secondary conveyor systems to load and discharge objects from a primary conveyor system.
Yet another disadvantage with such prior art conveyors is their relative complexity, especially in the reciprocating conveyor art. The article sensing device is conventionally separate and apart from the pusher or like transferring device. These devices are, in turn, separate and apart from the frame which supports the objects to be transferred. The result is a complex system consisting of many interrelated moving and stationary parts. This complexity results in frequent breakdown of the conveyor, thereby causing production delays and increased maintenance costs.